Tuesday, 20 March 2012

Insight Into a Shocking Therapy for Depression

Since the 1930s, doctors have been
jolting the brains of depressed patients with electricity to relieve
their symptoms. The treatment, known as electroconvulsive therapy
(ECT), works, but it can cause memory loss and confusion and lead to
difficulty forming new memories. Today, physicians generally limit it
to patients who are severely ill, including those at risk for suicide.
Now, a brain-imaging study highlights the part of the brain most
affected, perhaps pointing to safer, less-invasive ways to achieve the
same results.

Depression may be caused by an overactive brain, says physicist and
neuroscientist Christian Schwarzbauer of the University of Aberdeen in
the United Kingdom. "There may be so much internal communication that
the brain becomes preoccupied with itself, less able to process
information coming in from the outside world," he says, noting that
studies have found that people with depression have heightened
connectivity among brain networks involved in paying attention,
monitoring internal and external cues, remembering the past, and
controlling emotions.

In a 2010 study, psychiatrist Yvette Sheline and colleagues at
Washington University School of Medicine in St. Louis, Missouri, found
that these overactive networks converged on a common point
in a region called the dorsal medial prefrontal cortex. This common
point, dubbed the dorsal nexus, may "hot wire" the brain networks
together in a way that leads to depression, the authors hypothesized.
It may be this nexus that's affected by ECT, according to the new
findings. In a study led by psychiatrist Ian Reid of Aberdeen,
Schwarzbauer and colleagues performed functional magnetic resonance
imaging (fMRI) scans of nine depressed patients before and after ECT.
Rather than focusing on activity in previously suspected brain areas,
the researchers examined connectivity in the brain as a whole,
examining changes in blood oxygenation in about 27,000 points known as
voxels (the 3D imaging equivalent of pixels on a computer screen).
Voxels were considered to be highly connected if their changes in blood
oxygenation were strongly correlated—if one went up and the other went
up to a similar degree.

After
treatment with ECT, connectivity was dramatically decreased in one
cluster of voxels around an area called the dorsolateral prefrontal
cortex, the researchers report today in the Proceedings of the National Academy of Sciences.
Decreases in connectivity reflected improvements in symptoms, as
reported by the patients. The area of decreased connectivity includes
the dorsal nexus previously identified by Sheline and colleagues. This
finding indicates that ECT reduces the influence of the dorsolateral
prefrontal cortex on this nexus.

Because the dorsal nexus is a place where attention, memory, and
emotion all converge, its emergence as the target of ECT explains both
the therapy's success and the side effects of memory impairment, the
authors write.

"This is an important study. It provides insight into a likely
mechanism for ECT," Sheline says. She adds that both antidepressant
treatment and cognitive therapy have been shown to reduce excessive
connectivity in some areas.

But research psychologist Jennifer Perrin, co-author of the new
paper, cautions: "It still isn't known whether these approaches reduce
connectivity in the specific area that we found." She says further
research is needed to see whether this effect is unique to ECT or is a
feature of other treatments as well.
Perrin says the finding may open the door to treatments that target
the area more directly. For example, in transcranial magnetic
stimulation, a magnetic field is passed over the scalp above this part
of the brain; a similar study could explore whether this technique
could be made more effective. The authors' method of analyzing
connectivity could also be used to study other disorders, such as
schizophrenia, autism, or dementia, she says.